Progesterone and caspase-3 activation in equine cyclic corpora lutea.

This research article explores the role of a certain enzyme, caspase-3, in causing cell death in the corpus luteum (a temporary endocrine structure in the ovaries) in horses, and how this may be linked to the endocrine functions of the corpus luteum. The study gathered blood and luteal tissue samples from several cycling mares during breeding season and found significant increases in active caspase-3 in the corpus luteum during various stages of development and regression, suggesting that caspase-3 could play an important role in the natural breakdown of the corpus luteum.

Objective of the Study

• The primary aim of the study was to investigate if the caspase-3 enzyme mediates cell death within the cyclic luteal structures of horses and to understand the connection that this process may have to luteal endocrine function. The corpus luteum (CL), a temporary endocrine gland formed after ovulation, secretes progesterone which is vital for the process of implantation.

Methodology

• Blood and luteal tissues were collected from 38 randomly chosen mares during breeding season. The luteal tissues were divided into four categories: corpora haemorrhagica (CH; n = 7), mid luteal phase corpora lutea (Mid-CL; n = 17), late or regressing corpora lutea (Late-CL; n = 9), and corpora albicans (CA; n = 5).
• The concentration of progesterone in the plasma was determined using a radioimmunoassay, and caspase-3 processing and poly (ADP) ribose polymerase (PARP) degradation were assessed through western blotting.

Findings

• The study observed a significant increase in plasma progesterone from CH to Mid-CL, followed by a steep decline to Late-CL and CA.
• There was evidence of increased activation of the caspase-3 enzyme during the middle, late and regression phases of the CL compared to CH.
• Immunocytochemistry revealed a considerable increase in the expression of caspase-3 in large luteal cells in all phases when compared with CH.
• Moreover, the natural caspase-3 substrate, PARP, was significantly degraded from CH to CA which also supported the increased role of caspase-3.
• The ratio of full-length to degraded PARP decreased significantly from CH to Mid-CL, Late-CL, and CA.
• The drop in progesterone from Mid- to Late-CL matched with no further increases in apoptosis (cell death).

Conclusion

• The findings of the research suggest that the caspase-3 apoptosis effector might play a crucial role in the involution of luteal tissue in mares. However, the relationship with progesterone production still requires further investigation.